1. Field of the Invention
The invention relates to marine steering systems and, more particularly, relates to a method and apparatus for controlling operation of a steering vane or tab that counteracts externally imposed steering torques imposed on the outboard engine or other steering device of a vessel.
2. Discussion of the Related Art
Marine steering systems sometimes employ a moveable steering vane or tab that moves so as to counteract external forces imposed on the steering device of the vessel, reducing or negating the need for the operator to impose steering forces to counteract these forces. These devices most typically are used in conjunction with outboard engines, in which case the engine itself is the steering device and is steered by pivoting about a vertical axis. In this case, the steering vane typically is disposed within the slip stream of the propeller of the outboard engine to channel the water in the strip stream in a manner that opposes external forces imposed on the engine during operation. Publications describing these systems often refer to the actuated vane or tab as a trim tab. However, such a reference is not technically accurate when referring to tabs that pivot about a vertical axis because trim tabs most typically pivot about a horizontal axis to adjust the fore-to-aft orientation or “trim” of a boat. Accordingly, this document utilizes the term “steering vane” or “steering tab” to refer to a structure that pivots about an at least generally vertical axis or otherwise moves at least generally from side to side to counteract externally forces imposed externally on a rudder, outboard engine, or other steered device during operation.
Most steering vanes employed to date are operated mechanically and passively, such as by using the combination of a push pull cable and a passive hydraulic cylinder. One such vane is disclosed in U.S. Pat. No. 4,482,331, the subject matter of which is hereby incorporated by reference. Another example is disclosed in U.S. Pat. No. 4,349,341 (the '341 patent) to Morgan et al., the subject matter of which is also incorporated by reference. The '341 patent discloses the use of a control lever pivotally mounted to the steering control element of the boat. Movement of the lever in one direction or the other by the steering control element generates tensile forces in an appropriate control cable to pivot a steering vane.
One shortfall of the system disclosed in the '341 patent is the inclusion of a lost motion linkage between the steering arm and the control rod of the steering mechanism of a boat. The necessity of a lost motion linkage creates a lag in steering response, which can affect the handling of a boat. Another disadvantage of this type of system is that the lost motion linkage potentially allows the propulsion unit to be steered by external forces such as waves or current, which will cause course deviations. Passive systems also necessarily have limited effectiveness at counteracting forces imposed on the steering device.
Computer based actuator systems have been developed to in an attempt to address at least some the disadvantages of passive mechanical based systems. For instance, U.S. Pat. No. 4,787,867 (the '867 patent) to Takeuchi et al., discloses a steering vane or tab that is supported on the propulsion unit of a marine engine and that can be pivoted in a direction opposite to the operator's steering direction so as to create a hydrodynamic force to assist in the steering of a vessel immediately upon the detection of a given steering import force. The steering vane position, however, is determined by a computer system using a selected one of plurality of pre-mapped positions. Such a system is at the mercy of the accuracy of the pre-mapped positions and on the operator's ability to select the appropriate map. Furthermore, a computerized system of this type must be customized to particular boat characteristics such as engine and propeller characteristics, trim settings, and overall boat designs. Such a system therefore is relatively expensive and difficult to implement. It also cannot be used, without modification, on a variety of different vessels or retrofitted onto an existing vessel.
It thus would be desirable, in a marine steering system, to automatically actuate a powered steering vane to actively reduce or counteract the external forces imposed on the steering system of a boat or other marine vessel during operation.
It would also be desirable to provide a marine steering system which lacks a substantial lost motion connection in the actuating system for the steering vane or tab thereof and which, therefore, does not induce a lag to an operator-initiated steering command response.
It is yet further desirable to provide a steering vane actuator assembly that is versatile so as to be capable of being attached to or retrofitted on a variety of boats without reconfiguration.